Chorng Haur Sow

Large-scale synthesis and field emission properties of vertically oriented CuO nanowire films

Using a simple method of direct heating of bulk copper plates in air, oriented CuO nanowire films were synthesized on a large scale. The length and density of nanowires could be controlled by growth temperature and growth time. Field emission (FE) measurements of CuO nanowire films show that they have a low turn-on field of 3.5?4.5?V??m?1 and a large current density of 0.45?mA?cm?2 under an applied field of about 7?V??m?1. By comparing the FE properties of two types of samples with different average lengths and densities (30??m, 108?cm?2 and 4??m, 4 ? 107?cm?2, respectively), we found that the large length?radius ratio of CuO nanowires effectively improved the local field, which was beneficial to field emission. Verified with finite element calculation, the work function of oriented CuO nanowire films was estimated to be 2.5?2.8?eV.

Electrospun α-Fe2O3 nanorods as a stable, high capacity anode material for Li-ion batteries

α-Fe2O3 nanorods are synthesized by electrospinning of polyvinylpyrrolidone (PVP)/ferric acetyl acetonate (Fe(acac)3) composite precursors and subsequent annealing at 500 °C for 5 h. X-ray diffraction and Raman spectroscopy analyses confirm the formation of a hematite structure as the predominant phase. The electron microscopy studies show that the electrospun α-Fe2O3 nanorods are composed of agglomerates of nano-sized particles and the average diameter of the nanorods is found to be 150 nm. Li-storage and cycling properties are examined by galvanostatic cycling in the voltage range 0.005–3 V vs. Li at various current densities and it is complemented by cyclic voltammetry. The electrospun α-Fe2O3 nanorods exhibit a high reversible capacity of 1095 mA h g−1 at 0.05 C, are stable up to 50 cycles and also show high rate capability, up to 2.5 C. The high rate capability and excellent cycling stability can be attributed to the unique morphology of the macroporous nanorods comprised of inter-connected nano-sized particles, thus making electrospun α-Fe2O3 a promising anode material for Li-ion batteries.

Microstructuring of Graphene Oxide Nanosheets Using Direct Laser Writing

Graphene(G),a single atomiclayer ofaromatic carbon atoms,has attracted much attention recently owing to its fascinating properties such as massless fermions, ballistic electronic transport, and ultrahigh electron mobility. [1] Currently, there are many approaches to the synthesis of graphene ranging from chemical vapor deposition from hydrocarbon to solution phase methods involving the chemical exfoliation of graphite. [2] One commonly used solution-processing route to graphene involved the chemical reduction of graphene oxide (GO). GO is produced by the oxidative treatment of graphite. [2] The basal planes of GO are decorated with epoxide and hydroxyl groups, while carboxylic and carbonyl groups are located at the edges. These oxygen functionalities render GO hydrophilic and improve its solubility, however they destroy the aromaticity of the graphene framework. As a result, GO is insulating, and a chemical reduction and thermal annealing treatment is needed before electronic conductivity could be recovered. The presence of oxygen functional groups also reduces the thermal stability of GO relative to that of G, since GO can be thermally pyrolized at high temperatures and transformed into volatile carbonaceous oxides. The thermal instability of GO motivates us to consider a strategy for the microstructuing of GO nanosheets using laser-assisted etching. The microstructuring of GO is relevant to the challenges of lithographically patterning G, since GO and G are interconvertible to some extent. Recently, promising approaches for the patterned assemblies of G on substrates have been developed. [3–8] Micro-contact printing using molecular templates was used to transfer GO sheets onto the pre-defined areas of the substrate surfaces via electrostatic attachment. [3] Large-scale G films were recently synthesized on patterned nickel layers using chemical vapor deposition. [7] All the patterning methods reported so far involved conventional lithographic techniques or employment of masks for the definition of patterns on substrates. To date, there are few demonstrations of a maskless, direct ‘‘writing’’ pattern on G-related materials using electron beam or optical methods.

α-Fe2O3 nanotubes-reduced graphene oxide composites as synergistic electrochemical capacitor materials

We present a facile approach for the fabrication of a nanocomposite comprising α-Fe(2)O(3) nanotubes (NTs) anchored on reduced graphene oxide (rGO) for electrochemical capacitors (ECs). The hollow tubular structure of the α-Fe(2)O(3) NTs presents a high surface area for reaction, while the incorporation of rGO provides an efficient two-dimensional conductive pathway to allow fast, reversible redox reaction. As a result, the nanocomposite materials exhibit a specific capacitance which is remarkably higher (~7 times) than α-Fe(2)O(3) NTs alone. In addition, the nanocomposites show excellent cycling life and large negative potential window. These findings suggest that such nanocomposites are a promising candidate as negative electrodes in asymmetrical capacitors with neutral electrolytes.

Morphologically robust NiFe2O4 nanofibers as high capacity Li-ion battery anode material.

In this work, the electrochemical performance of NiFe2O4 nanofibers synthesized by an electrospinning approach have been discussed in detail. Lithium storage properties of nanofibers are evaluated and compared with NiFe2O4 nanoparticles by galvanostatic cycling and cyclic voltammetry studies, both in half-cell configurations. Nanofibers exhibit a higher charge-storage capacity of 1000 mAh g(-1) even after 100 cycles with high Coulmbic efficiency of 100% between 10 and 100 cycles. Ex situ microscopy studies confirmed that cycled nanofiber electrodes maintained the morphology and remained intact even after 100 charge-discharge cycles. The NiFe2O4 nanofiber electrode does not experience any structural stress and eventual pulverisation during lithium cycling and hence provides an efficient electron conducting pathway. The excellent electrochemical performance of NiFe2O4 nanofibers is due to the unique porous morphology of continuous nanofibers.

The manipulation and assembly of CuO nanorods with line optical tweezers

We present a simple technique for manipulating and assembling one-dimensional (1D) CuO nanorods. Our technique exploits the optical trapping ability of line optical tweezers to trap, manipulate and rotate nanorods without physical contact. With this simple and versatile method, nanorods can be readily arranged into interesting configurations. The optical lin et weezers could also be used to manipulate an individual nanorod across two conducting electrodes. This work demonstrates the potential of optical manipulation and assembly of 1D nanostructures into useful nanoelectronics devices. M This article features online multimedia enhancements (Some figures in this article are in colour only in the electronic version)

Tensile test of a single nanofiber using an atomic force microscope tip

In this study, an approach using an atomic force microscope (AFM) tip to stretch a single electrospun polyethylene oxide (PEO) nanofiber is demonstrated. One end of the nanofiber is attached to a movable optical microscope stage and the other end of the nanofiber to a piezoresistive AFM cantilever tip. The nanofiber is stretched by moving the microscope stage and the force is measured via the deflection of the cantilever. The elastic modulus of PEO nanofiber is found to be about 45MPa.

Plasmon-Enhanced Photocatalytic Properties of Cu2O Nanowire–Au Nanoparticle Assemblies

Cu(2)O-Au nanocomposites (NCs) with tunable coverage of Au were prepared by a facile method of mixing gold nanoparticles (Au NPs) with copper(I) oxide nanowires (Cu(2)O NWs) in various ratios. These Cu(2)O-Au NCs display tunable optical properties, and their photocatalytic properties were dependent on the coverage density of Au NPs. The photocatalytic activity of Cu(2)O-Au NCs was examined by photodegradation of methylene blue. The presence of Au NPs enhanced the photodegradation efficiency of Cu(2)O NCs. The photocatalytic efficiency of Cu(2)O-Au NCs initially increased with the increasing coverage density of Au NPs and then decreased as the surface of Cu(2)O became densely covered by Au NPs. The enhanced photocatalytic efficiency was ascribed to enhanced light absorption (by the surface plasmon resonance) and the electron sink effect of the Au NPs.

Cobalt-based compounds and composites as electrode materials for high-performance electrochemical capacitors

Transition metal compounds (oxides, hydroxides, etc.) are emerging electrode materials for electrochemical capacitors (ECs) due to their rich redox properties involving multiple oxidation states and different ions. Pseudocapacitance derived from the reversible faradaic reactions can be ten times higher than those of the state-of-the-art carbon-based electric double layer capacitors (EDLCs). As one of the most well-known electroactive inorganic materials, extensive studies of cobalt-based compounds (Co3O4, Co(OH)2, CoOOH, CoS, etc.) for ECs have mushroomed, and the relevant literature has grown exponentially in the past ten years. This review consolidates and evaluates the recent progress, achievements, weaknesses and challenges in the research of cobalt-based compounds and nanocomposites for ECs. The triangular relationship between synthesis strategies, tailored material properties and the electrochemical performances is thoroughly assessed, unveiling the advanced electrode material design and development.

The National University of Singapore nuclear microscope facility

Abstract The National University of Singapore nuclear microscope facility is based around a HVEC AN2500 single ended Van de Graaff accelerator and an Oxford Microbeams coupled quadrupole triplet focusing system. Particle induced X-ray emission (PIXE), nuclear or Rutherford backscattering spectrometry (RBS) and scanning transmission ion microscopy (STIM) can be carried out simultaneously. Data acquisition is carried out using a simple but flexible PC based system (Oxford Microbeams DAQ) and the data is analysed using a combined RUMP and GUPIX PC based interactive package (NUSDAN) acting under WINDOWS. Resolution tests using a calibration grid and a multi layer integrated circuit have shown the facility to be capable of 600 nm spot sizes for 2 MeV protons at currents suitable for microanalysis.